Other astronomers call the technique original and inventive, if a little
unorthodox.

“Paula Jofré impressed me as beingvery innovative,” says astronomerKenneth Freeman of the AustralianNational University in Canberra. “Shesees things that other researchers donot see.”Payel Das of the University of Oxford,a collaborator on the Milky Way proj-ect and a close friend, calls Jofré “reallybrave” as a researcher. “She’s very con-fident, which is really nice. I thinkespecially now — we’re going throughthis crisis of women in physics andscience and all this— we need thisconfidence.”Jofré has never shied away fromunpopular paths. Before she graduatedfrom an all-girls high school in Santiago,a guidance counselor spoke to her classabout the importance of choosing acareer that would leave time for family.One shouldn’t choose a career in, say,astronomy.

“The whole class looked at me,” says
Jofré, who had been interested in astronomy since childhood. The moment only
strengthened her resolve. “This woman
trying to say, ‘please don’t do that,’ was
for me an argument to say, ‘please do it.’ ”
The question of whether astronomy is
compatible with a family came up sooner
than Jofré expected: Her first child was
born before she and her partner, Thomas
Maedler, finished their Ph.D.s. Their
second was born during her first postdoctoral fellowship. Being the only
parents in their graduate cohort was difficult. “You feel quite lonely when you’re
the only one,” Jofré says.

But contrary to the guidance coun-selor’s warnings, parenthood has beengrounding for the two and helped keepthem focused on what’s important—“which is not like, papers, papers, papers,papers, papers,” as Maedler puts it.“We’re always this little nucleus, thefour of us, this little atom that is walk-ing around.”For Jofré, science has been inextrica-bly entwined with family — not just thesun’s, but her own. s

All in the family Paula Jofré
and colleagues mapped out chemical
relationships between the sun and

21 of its sibling stars. Three main
branches emerged: younger stars
in the Milky Way’s thin disk (red,
including the sun), much older stars
that could be in the Milky Way’s
more dispersed thick disk (dark
blue) and a third branch that lies
in between (light blue). Six stars
(black) had no clear relationship to
the others, but more observations
could help tie them in.

their results. There, she met Cambridge
anthropologist Robert Foley, who
showed her how evolutionary trees can
trace relationships of members of a species over time. Suddenly she realized
that stars, too, pass down bits of themselves to successive generations. Perhaps, she thought,
these generations could
also be traced back in time.

Soon, she and Foley
hashed out the stellar
family tree project at dinner in a Cambridge dining
hall— “very much like a
Harry Potter room,” she
says, where all the fellows
wear academic gowns. Stars
obviously don’t procreate
like animals, the pair agreed, but dying
stars do pass on their chemistry.

That happens because stars forge
heavy elements, such as carbon and iron.
When the stars die, they often explode
and spread those elements throughout the cosmos. The next generation
of stars, born from collapsing clouds of
gas containing those elements, picks up
elements from the earlier generation.

And thus a family is born. Stars from
the same gas cloud should have almost
identical chemistry, something like how
siblings have similar DNA. The analogy
is close enough that Jofré, Foley and
colleagues built a three-branched tree
showing the relationships
of 21 of the sun’s sibling
stars in 2017 in the Monthly
Notices of the Royal
Astronomical Society. The
team also reported that
two of the branches were
known groupings — one was
the Milky Way’s thin disk of
stars, and the other was the
older thick disk that surrounds it.

The third branch revealed
new connections, showing that Jofré’s
technique does more than map known
star relationships. The approach can
reveal new information about past stellar nurseries.

By expanding to more groups of stars,
“we could use these trees to learn something about the evolution of our whole
galaxy,” Jofré says. “That has been
so exciting.”